The present invention relates, generally, to transportation systems and processes, and in particular embodiments, to ground-based transportation systems and processes employing magnetically levitated vehicles for transportation of freight or passengers. Preferred embodiments are configured for relatively low-cost and energy efficient implementations.
It is widely recognized that transportation of freight and passengers is a necessary component of modern economic societies. In the last century, significant advances have been made with respect to speed and efficiency of transportation systems. Such advances have been driven, at least in part, by economic demand. Indeed, high-speed transportation of freight and passengers has long been recognized as having significant economic value. This is evidenced by the widespread use of air transportation and increasing use of high-speed rail in both freight and passenger markets.
However, there are a number of shortcomings of conventional transportation systems. Traditional high-speed rail systems require mechanical contact between wheels and rail, giving rise to wear, frictional losses of energy and vibrations. In addition, conventional air and rail systems experience significant aerodynamic drag, which increases energy costs. Moreover, modern air transportation requires human pilots, ground control systems, and expensive airports. Past efforts to address some of those shortcomings have included efforts to develop a practical magnetically levitated train system.
Magnetically levitated (maglev) vehicles have long been proposed for high-speed transportation. Several prototypes of such systems have been developed that would require costly infrastructure in the form of heavy and precise track systems or expensive superconducting magnets. In some prior systems, massive trains have been proposed, requiring massive, expensive infrastructure. In addition, prior systems have employed relatively complex geometries, due to a perceived necessity to provide horizontal surfaces to create levitation forces and vertical surfaces to create lateral forces. Moreover, since electromagnets can only generate attractive forces, some proposed systems have included vehicles configured with awkward and heavy structures that reach underneath an iron rail to create lift. Furthermore, many of the previously proposed magnetically levitated transportation systems are designed to operate in an open or ambient atmosphere, such that aerodynamic drag can be a major factor contributing to energy consumption.
An understanding of magnetically levitated transportation involves a basic understanding of the magnetic forces that can be created by the interaction of permanent magnets. For example, it is well known that opposite magnetic poles provide an attraction force and like poles provide a repelling force. A magnetic field can produce a force on a current carrying conductor, typically referred to as a Lorentz force.
A force is also created in a magnetic gap between two iron pole faces. Such a force, known as the Maxwell force, is proportional to the square of the magnetic field. In some magnetic actuators, such as variable reluctance motors, salient or toothed poles are used to create Maxwell forces parallel to the pole faces. Actuators that are based on this principle are typically referred to as salient pole Maxwell actuators. Magnetic induction is another means of producing magnetic force. By moving a magnetic field source rapidly over a conductive sheet, an image of the magnet source is created in the sheet. Since the image of a magnetic pole has the same polarity as the magnetic pole itself, a repulsion force is created.
Prior magnetically levitated train systems have been proposed, wherein some of those principles of magnetic forces are employed. For example, in U.S. Pat. No. 5,601,029, to Geraghty et al., a permanent magnet rail array is used for levitation and Maxwell force actuators are used for lateral and yaw stabilization. The Maxwell force actuators interact with an iron side-rail with high loads. The side-rails described in the Geraghty et al. patent would tend to add considerable cost and weight to the overall guide-rail system. In addition, due to the geometry of the permanent magnets described in the Geraghty et al. patent, the levitation function requires a relatively large mass (and weight) of magnets, thus, resulting in a relatively costly implementation of the design.
Also, in U.S. Pat. No. 4,486,729 to Lee, a permanent magnet rail array is used for levitation and mechanical bushings are used for lateral and yaw control. While the loading on the mechanical bushings is small relative to the levitation force, this system is subject to wear and not likely suitable for high-speed use. A similar approach is taken in U.S. Pat. Nos. 5,165,347 and 3,158,765.
In U.S. Pat. No. 4,356,772 to van der Heide, a permanent magnet rail array is used for levitation and periodic vertical forcing is used to create dynamics described by the Matthieu equation. Such an arrangement can be sensitive to variations in load mass and may not be sufficiently robust for commercial use.
In U.S. Pat. Nos. 5,440,997 and 4,805,761, permanent magnet levitation is employed, where a shear displacement between magnets is created during vehicle motion and a resulting shear restoring force is supplied by the permanent magnet interaction. Air bearings and bushings are used (respectively) in these two patents for lateral stabilization. Air bearings require relatively small gaps for operation and are thus subject to mechanical contact and, thus, wear, when there are variations in the track surface.
In U.S. Pat. No. 3,899,979 to Godsy, Maxwell force levitation actuators are employed. Those actuators rely on reluctance centering of actuator teeth for lateral stabilization. In addition, the actuators on the Godsy system are overhung and require additional support structure on the vehicle, resulting in a relatively high cost system. Moreover, the large amount of iron in this system can add considerable weight to the vehicle.
The system described in U.S. Pat. No. 3,937,148 to Simpson uses Maxwell force levitation and guidance actuators. The Simpson system requires a relatively large amount of iron on the vehicle and track, as the guidance actuators employ a vertical iron surface for actuation. Similar limitations are encountered in the systems described in U.S. Pat. Nos. 5,243,919, 4,646,651, and 3,976,339, where large lateral forces must be accommodated with heavy, relatively expensive structural elements.
The system described in U.S. Pat. No. 5,433,155 to O""Neill et al. uses Lorentz force actuators. One embodiment uses permanent magnets to produce the fields that interact with electrical currents. Lorentz force actuators supply vertical forces in this design so that high currents are needed in coils. Such a scheme is less efficient than one that employs permanent magnets for levitation. Moreover the O""Neill et al. system requires complex interleaved track and vehicle components.
A common feature of such prior designs is that the vehicle structure wraps partially around the track structure or the track structure wraps partially around the vehicle structure. Such structures can be complex and heavy, as they support high loads applied to cantilevered substructures. An indication of the complexity of these systems is that there is no single plane that separates the vehicle magnetic components from the track magnetic components. This follows from the use of both vertical and horizontal magnetic gaps in such designs. Simpler transportation systems have used wheeled vehicles on a road or guideway, where the road defines a plane in contact with the vehicle wheels.
Embodiments of the present invention relate, generally, to magnetic levitation transportation systems and processes which address some or all of the problems noted above with respect to conventional magnetic levitation systems. For example, an advantage, according to various embodiments of the invention, relates to a relatively simple structural configuration wherein permanent magnets are employed on a vehicle for providing (or contributing to) levitation and electromagnets are employed on a vehicle for providing (or contributing to) lateral control of the vehicle relative to a guideway array of magnets.
A further advantage, according to various embodiments of the invention, relates to magnetic levitation transportation systems and processes that employ a relatively simple structural configuration that avoids the need for complex lateral support structure on the guideway. Instead, lateral and vertical control is provided with a simplified guideway and vehicle structure in which a separation plane separates the vehicle magnetic components from the track magnetic components during levitation of the vehicle, where the separation plane does not pass through or contact either the guideway structure or the vehicle structure.
A further advantage, according to various embodiments of the invention, relates to magnetic levitation transportation systems and processes that make efficient use of magnetic field energy from permanent magnets by employing magnet materials or arrays that have a rotating magnetization, to provide (or contribute to) levitation of a vehicle over a guideway. For example, embodiments of the invention employ one or more guideway magnet arrays having rotating magnetization, wherein the magnetization vector of the array (or material) rotates in a consistent direction when viewed in section and within increments of less than 180 degrees including the limiting case where the increments are infinitesimal and the rotation is continuous. Further embodiments employ one or more guideway magnet arrays having counterclockwise rotating magnetization when viewed left to right with the interfacing (or xe2x80x9cactivexe2x80x9d) surface is facing upward. Further references herein to xe2x80x9ccounterclockwise rotationxe2x80x9d will be understood to refer to the direction of rotation, when viewed as noted above. If the active surface is facing downward, as is the case with vehicle magnets, then the magnetization rotation direction is counterclockwise, when viewed from the right to the left side of the array. Preferred embodiments employ one or more Halbach arrays with rotating magnetization. Such rotating magnetization arrays (and, in particular, Halbach arrays) allow magnetic field energy to be more efficiently directed on one side (the active side) of the array.
A further advantage, according to various embodiments of the invention, relates to magnetic levitation transportation systems and processes that make efficient use of magnetic field energy from permanent magnets by employing magnet arrays (or materials) that have stronger magnets (or magnetic field energy) in the central portion of the array (or material), than at the lateral sides of the array (or material). For example, various embodiments of the invention employ magnet arrays having larger (thicker) magnets in the central portion of the array and smaller (thinner) magnets at the lateral sides of the array. In some embodiments, a cross-section shape of such an array resembles a cup shape or inverted cup shape. Such cup-shaped arrays may be employed as vehicle magnets and/or guideway magnets.
A further advantage, according to various embodiments of the invention, relates to a relatively simple structural configuration that employs two distinct sub-arrays of guideway magnets. Similarly, various embodiments of the invention employ two distinct sub-arrays of vehicle magnets for interaction with guideway magnets to provide (or contribute to) levitation of the vehicle relative to the guideway magnets. In yet further embodiments, each sub-array of guideway magnets interacts with at least one permanent magnet (or magnet array) on the vehicle and at least one electromagnet (or control coil array) on the vehicle.
Further advantages relating to cost, weight and power efficiency may be achieved, according to yet further embodiments of the invention, for example, by employing relatively lightweight capsules dispersed along guideways. Further efficiencies may be achieved by employing configurations that allow the generation of both levitation and lateral forces from the same guideway magnet array (or rail). Yet further efficiencies may be achieved by employing optimized Halbach or rotating magnet array structures, for example, to minimize the amount of permanent magnet material used in the guideway magnet array. In yet further embodiments, cup-shaped magnet arrays may be employed to minimize overall guideway array (or rail) weight, while maintaining the same lift capability.
In yet further embodiments, further power efficiencies may be achieved by employing only permanent magnets to provide levitation force (or the majority of the levitation force) for levitating the vehicle relative to the guideway and operating the vehicle in a vacuum (or partial vacuum). For example, the vehicle may be levitated and propelled with a tube-shaped guideway structure that is evacuated (or partially evacuated).